1. Field of the Invention
This invention generally relates to liquid crystal display (LCD) and integrated circuit (IC) fabrication and, more particularly, to a silicon film and fabrication process to laser irradiate silicon film in making polycrystalline silicon thin film transistors (TFTs) for Active Matrix (AM) LCDs.
2. Description of the Related Art
Lateral crystallization by excimer-laser anneal (LC-ELA) is a desirable method for forming high quality polycrystalline silicon films having large and uniform grains. Further, this process permits precise control of the grain boundary locations.
FIG. 1 is partial cross-sectional view illustrating the topography of laser-irradiated domains (prior art). After the completion of lateral growth, the two crystal fronts meet at the center of the domain 200 where explosive nucleation occurs. The stepping distance of the beam is a crucial factor in the process throughput and, hence, the economics of the LC-ELA process in mass productions. The stepping distance, in turn, is dependent upon the lateral growth length (LGL). LGL is affected by the transient temperature profile of the film, which defines the time for the lateral propagation of the two facing crystal fronts, before the remaining molten volume becomes cold enough to trigger copious (explosive) nucleation.
It would be desirable to improve the lateral growth length (LGL) during crystallization. Such improvement would enable an increase of the stepping distance between successive shots.
It would be advantageous if the melt duration of the laser-irradiated volume of silicon film could be increased, to gain a corresponding increase in the LGL.